The electromagnetic spectrum is arranged in order of increasing wavelength (or decreasing frequency) as follows: Gamma rays < X-rays < Ultraviolet < Visible < Infrared < Microwaves < Radio waves.

1. Gamma-rays: Wavelength range $\sim < 10^{-3} \text{ nm}$ (Shortest).
2. X-rays: Wavelength range $\sim 1 \text{ nm}$ to $10^{-3} \text{ nm}$.
3. Ultraviolet rays: Wavelength range $\sim 400 \text{ nm}$ to $1 \text{ nm}$.
4. Microwaves: Wavelength range $\sim 0.1 \text{ m}$ to $1 \text{ mm}$.

Among the given options, Gamma-rays possess the highest frequency and energy, and consequently, the shortest wavelength.